© 1991-2011 Jerry Emanuelson


In ordinary language, tea is often used to mean any beverage produced from the leaf of any plant.  Technically, tea comes from the leaf of one particular plant.  The same plant is the source of green tea, as well as the black tea that is much more popular in the U.S.

Tea is more widely consumed than any beverage in the world other than water.  Most tea consumed is black tea, which is produced by a process which oxidizes the green leaf.  This process enhances the taste, but destroys most of an important class of chemicals called green tea polyphenols (GTP).

GTP has been widely studied in recent years and appears to be an important substance for the chemoprevention of cancer.  In March, 1991 an important medical conference on green tea was held in New York, The First International Symposium on the Physiological and Pharmacological Effect of Camellia Sinensis (Tea).  Titles of some of the reports presented at that symposium included:

  • 1.   On the Role of Tea in Modifying Causes of Major Human Cancers

  • 2.   Effects of Green Tea and Its Components on Lung Tumorigenesis Induced by a Tobacco-Specific Nitrosamine

  • 3.   Tea, Fluid Balance, and Renal (kidney) Disease

  • 4.   Protection against Cancer Risk by Japanese Green Tea Tea Polyphenols as Antioxidants

  • 5.   Inhibition of in Vitro Neoplastic Transformation by Tea Ingredients

  • 6.   The Effects of Tea Polyphenols on Cardiovascular Diseases

  • 7.   A Study on Tea Pigment in the Prevention of Atherosclerosis

(The summaries of these papers were published in the scientific journal, Preventive Medicine Vol. 21, pp. 331-333, 1992)

Report 3 found no adverse effects of tea on kidney function except for a very few persons with terminal kidney diseases.  The other reports showed very positive effects for tea extracts.

A number of complete reports on Green Tea Polyphenols were published in subsequently published in Preventive Medicine during 1992 showing the beneficial effects of green tea on cancer and coronary artery disease.  A report in the October, 1992 issue of Comprehensive Therapy (pp. 3-8) "Green Tea in the Chemoprevention of Cancer," covered the effectiveness of GTP in preventing a wide variety of cancers.

The cancers that GTP can prevent in humans include the deadliest cancers such as those of the liver, lungs, colon, and pancreas.  In addition, green tea has been show to be very effective at preventing tooth decay and killing some types of stomach viruses.  Green Tea Polyphenols are present in commercially available green teas such as the Lipton's Green Tea sold in most grocery stores and other brands sold in health food stores.  Oolong tea is partially oxidized green tea and contains about 20-30 percent of the GTP concentration of green tea.  Green and black teas may also be mixed to obtain both the flavor of black tea and the health benefits of green tea.  Green Tea Extract capsules containing 20 percent to 80 percent Green Tea Polyphenols are available from several supplement manufacturers.

The optimal daily dose of Green Tea Polyphenols is not yet known. Commercially available GTP capsules are typically equivalent to five or more cups of tea, yet even one cup of green tea daily seems to confer some benefit.  Ideally, however, Green Tea Polyphenols should be consumed several times a day since the lifetime of Green Tea Polyphenols in the body is very short.

All tea contains oxalates that may cause kidney stones.  The most common type of kidney stone is the calcium oxalate stone formed in the kidney when soluble oxalates combine with soluble calcium compounds to form the highly-insoluble calcium oxalate.  The probability of tea causing kidney stones can be dramatically reduced by ingesting some form of calcium along with the tea in order to form the calcium oxalate in the digestive tract (where it cannot be absorbed and will pass through), rather than in the bloodstream or the kidney.

(An additional warning for sufferers of kidney stones:   The food with the highest oxalate content is spinach.  Spinach contains so much oxalate that spinach processing equipment sometimes gets clogged up with insoluble oxalates.)

In some rare individuals, the consumption of large amounts of green tea has been associated with liver damage.  Individuals who have liver problems or who are taking medications that stress the liver should consider taking 1000 to 2000 mg. of the nutrient N-Acetyl-Cysteine to prevent liver damage, and should monitor liver function regularly.

Since the original publication of this chapter, a large number of new scientific studies have continued to find beneficial effects of green tea in preventive medicine.  In addition, green tea has become much more widely available in the United States as these studies have become more widely publicized.  In addition, pre-made green tea drinks have become widely available.  These pre-made green tea drinks are very convenient, but they are nearly all pre-sweetened.  This means that the buyer of these pre-made green tea drinks must carefully read the ingredients.  The green tea drinks sweetened with sugar or high-fructose corn syrup are likely to do more harm to one's health than good.

The pre-made drinks sweetened with sucralose (Splenda®), though, are probably very beneficial.  Although some people are suspicious of all artificial sweeteners, there is no doubt that sucralose is much better than rapidly-absorbed carbohydrates, and the convenience of these pre-made green tea drinks encourages people to drink green tea several times a day -- in a way that more closely matches the intake pattern of those individuals in countries that have been getting the benefits of green tea for centuries.  It is doubtful if any of these bottled green tea products can match the polyphenol content of freshly-brewed green tea, but they are much better than most of the other alternatives.  A much better alternative to conventional sugars is the use of the combination of stevia and erythritol.  This stevia/erythritol combination is more difficult to find, but green tea (and other beverages) are being made using this combination.

Fresh-brewed green tea is definitely superior to the bottled green-tea drinks, but the bottled green tea drinks are often used by people who would never drink green tea otherwise.  The amount of beneficial polyphenols is nearly always less in bottled green tea than in fresh-brewed green tea.  More importantly, consumers need to be aware of the enormous variability in the amount of beneficial polyphenols in various brands of bottled green tea, as well as the fact that the polyphenols in bottled green tea deteriorate with age.

At an August 2010 meeting of the American Chemical Society, Dr. Shiming Li and Professor Chi-Tang Ho presented their findings that in bottled green tea drinks, the polyphenol levels were 81, 43, 40, 13, 4, and 3 milligrams of polyphenols in various brands per 16 ounce bottle.  The range of 3 to 81 milligrams is a huge difference.  Because green tea polyphenols tend to taste bitter, some manufacturers make bottled green tea that is extremely weak tea.  Other manufacturers try to cover up the slightly bitter taste with excessive amounts of sweeteners.  Since consumers don't have a way to measure the polyphenol level, they should choose only bottled green tea that looks like it has not been watered down, and that even tastes a little bitter.  Brands that are watered down or taste excessively sweet are unlikely to contain much of the beneficial green tea polyphenols.  (The watered-down brands are often fairly obvious just by looking at them in the store.)

Of course, the best option is still to brew the green tea yourself.

Additional recent references.

Venables, Michelle C., Hulston, Carl J., Cox, Hannah R., and Jeukendrup, Asker E.  Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans.  American Journal of Clinical Nutrition. 2008, March, Vol. 87, No. 3, pp. 778-784.

Moore, R.J., Jackson, K.G., and Minihane, A.M.  Green tea (Camellia sinensis) catechins and vascular function.  British Journal of Nutrition. 2009, December. Vol. 102. Issue 12. pp. 1790-1802.

Shen, C.L., Yeh, J.K., Cao, J.J. and Wang, J.S.  Green Tea and bone metabolism.  Nutrition Research. 2009 July. Vol. 29. Issue 7 pp. 437-56.

Phung O.J., Baker W.L., Matthews L.J., Lanosa M., Thorne A., and Coleman C.I.  Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis.  American Journal of Clinical Nutrition. 2010, January. Vol. 91. Issue 1. pp. 73-81.

Butt, M.S., and Sultan, M.T.  Green tea: nature's defense against malignancies.  Critical Reviews in Food Science and Nutrition. 2009 May. Vol. 49. Issue 5. pp. 463-473.

Shankar S., Ganapathy S., Srivastava R.K.  Green tea polyphenols: biology and therapeutic implications in cancer.  Frontiers in Bioscience 12. 2007, September 1. pp. 4881-4899.

Tachibana, H.  Molecular basis for cancer chemoprevention by green tea polyphenol EGCG.  Forum of Nutrition. 2009. Vol. 61. pp. 156-169.

de Mejia, E.G., Ramirez-Mares, M.V., and Paungpraphant, S.  Bioactive components of tea: cancer, inflammation and behavior.  Brain, Behavior and Immunity. 2009, August. Vol. 23. Issue 6. pp. 721-731.

Arab, L., Liu, W. and Elashoff, D.  Green and black tea consumption and risk of stroke: a meta-analysis.  Stroke. 2009, May. Vol. 40. Issue 5. pp. 1786-1792.

Thielecke F. and Boschmann M.  The potential role of green tea catechins in the prevention of the metabolic syndrome - a review  Phytochemistry. 2009, January. Vol. 70. Issue 1. pp. 11-24.

Basu, A. and Lucas, E.A.  Mechanisms and effects of green tea on cardiovascular health.  Nutrition Reviews. 2007, August. Vol. 65. Issue 8 part 1. pp 361-375.




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